1. Field of the Invention
This invention relates to the removal of noxious components, such as nitrogen oxides, sulfur oxides, particulate matter and carbon monoxide, from effluent gases produced by industrial processes for purposes of meeting air quality standards and air pollution emission regulations.
Existing scrubbers utilize short residence times, on the order of less than 5 seconds, and high energy levels to achieve intimate contact between noxious molecules in the gas and the scrubbing liquid intended to remove these molecules so as to reduce equipment size and cost and meet space limitations. Because of the short residence time, certain innovative removal processes cannot be made to work effectively.
Since the time required to achieve complete reaction is directly related to the chemical concentration, existing short residence time scrubbers can only work effectively at higher concentrations of noxious components and involve complex reactions requiring high concentrations of chemicals in the liquid to effect removal of the noxious components. The high concentrations of these chemicals increase the operational costs and produce byproducts that are either difficult to dispose of or to sell.
Additionally, the manufacturing cost of short residence time scrubbers is very high due to the need for high strength, rigid, corrosion-resistant materials required to meet the high pressure, high energy conditions within the scrubber and to withstnad the corrosive effect of the high concentrations of reactive chemicals.
2. Description of the Prior Art
U.S. Pat. No. 3,701,235 discloses a method and apparatus for removing foreign constituents from a gas by inducing flow of the gas through an elongated, inflatable treatment chamber and washing and drying the gas as it passes therethrough. The composition of the washing liquid is not described although water is mentioned or inferred in most of the claims.
U.S. Pat. No. 4,164,547 describes a process for removing sulfur dioxide from waste gas from coal and liqnite combustion in a wet scrubber incorporating a control system to maintain suitable levels of alkali reactants produced from fly ash, e.g. calcium, sodium and magnesium ions.
U.S. Pat. No. 4,325,713 describes a process and apparatus for removal of sulfur oxides and fly ash particulates incorporating an absorber and a spray dryer and utilizing complex chemical reactions utilizing sodium hydroxide, sodium carbonate and sodium bicarbonate.
U.S. Pat. No. 4,228,139 describes a process for removing sulfur oxides from flue gas utilizing a high ionic strength slurry produced from the fly ash of coal fired boilers maintained at a pH of about 4 and incorporating a venturi and multiple spray chamber scrubber.
U.S. Pat. No. 4,002,724 describes a method for removing sulfur dioxide from waste gas utilizing a slurry produced from the fly ash from lignite based fuel combustion and incorporating particle size classification and size reduction equipment.
U.S. Pat. No. 3,632,306 describes a process for removing sulfur oxides from waste gas utilizing a slurry containing calcium, magnesium and barium oxide or carbonate particles with an acidic radical additive.
U.S. Pat. No. 3,708,266 describes an apparatus for removing sulfur dioxide from flue gas utilizing an absorbent slurry and incorporating a grinding mill to reactivate the particles in a recycled slurry.
U.S. Pat. No. 3,520,649 describes a typical apparatus for removing sulfur oxides utilizing a limestone or dolomite slurry in a spray drier type apparatus.
From the foregoing, it will be clear that there still exists a need for a low cost, economical system which effectively removes noxious gases, particularly nitrogen oxides, from industrial effluent gaseous waste streams.